Affinity-purified anti-ubiquitin antibodies from sheep have been developed and characterized, and have been used in a number of applications. These applications include: (1) use as a probe to detect endogenous ubiquitin and ubiquitin-protein conjugates in Western blotting of tissue lysates, (2) use as reagents for immunocytochemical analysis of thin sections of brain and eye lens, and (3) when coupled to a solid support, use as an immunoaffinity chromatography matrix. Other work has centered on developing a purification scheme for "ubiquitin activating enzyme", El, from human blood.